1. Field of the Invention
This invention relates to a process for producing hydrogen by reacting carbon monoxide with steam at elevated temperatures in the presence of a catalyst containing at least one alkali metal compound, at least one metal hydrogenation-dehydrogenation component and a halogen moiety. More particularly, the invention relates to an improved water gas shift catalyst that contains a halogen constituent, preferably chemically combined chlorine, in combination with an alkali metal salt derived from a weak acid and at least one metal hydrogenation-dehydrogenation component and processes utilizing the chlorine-containing catalyst for the production of hydrogen.
2. Description of the Prior Art
The water gas shift reaction is widely used in commerce and is typically promoted with catalysts based on combinations of iron oxide with chromia or mixtures of copper and zinc materials. The currently used commercial shift catalysts suffer from a number of deficiencies, the principal deficiency being the inability of the available catalysts to promote the shift reaction to high conversion levels when the process is conducted at low temperatures in the presence of sulfur and/or halogen impurities.
One of the inventors named herein has discovered that the problems encountered with the use of prior art water gas shift catalysts could be overcome by utilizing a shift catalyst based on a combination of an alkali metal compound derived from an acid having an ionization constant less than about 1 .times. 10.sup.-.sup.3 with at least one metal hydrogenation-dehydrogenation component. It was found that unusually effective results could be secured with this catalyst when the weight ratio of the hydrogenation-dehydrogenation component to the alkali metal compound, each measured on the basis of the oxide thereof, present in the catalyst is maintained at levels of less than about 10 : 1, preferably less than about 5 : 1, and most preferably less than 3 : 1. The activity of this type of catalyst was found to be further enhanced when at least a portion of metal hydrogenation-dehydrogenation component and/or alkali metal compound are present in the catalyst in a sulfide form. However, the very high activity level secured with the sulfided catalyst slowly degrades with use unless the feedstock being processed contains at least minor amounts of sulfur constituents.
Shift catalysts containing metallic hydrogenation-dehydrogenation components in combination with minor amounts of alkali metal materials have been described in British Pat. No. 961,860 and U.S. Pat. No. 3,529,935. Numerous other references exist that disclose catalyst combinations made up of heavy metal compositions in conjunction with an alkali material. Exemplary of such teachings are the disclosures of Switzerland Pat. No. 69,336; U.S. Pat. Nos. 1,330,772; 3,518,208; 3,490,872; 1,896,840; 2,147,780; 2,364,562; Ztschr. Elektrochem 44 (1938), pp. 577-578; Netherlands application No. 66,01536; Japanese Pat. No. 129,729; Russian Pat. No. 67,942; French Pat. Nos. 777,546 and 815,351; Austrian Pat. Nos. 149,657 and 153,165; German Pat. No. 706,868; Belgian Pat. No. 659,421 and Simck et al., Zprary Ustava Ved. Vyk. Uhli Praze, 2 (1935) pp. 113-128 (see also Chem. Abs., 30 (1936)).